The invention concerns a data carrier such as a security, banknote, identity card or similar which features embossing in a predefined area.
It has long been usual to give securities, such as shares for example, an embossing. Such an embossing introduced into the paper is usually described as blind embossing. Common principles have even been drawn up by the German securities exchanges for the printing of securities (xe2x80x9cstock exchange guidelinesxe2x80x9d) which stipulate certain basic requirements for the form and execution of such embossings. For example, according to these stock exchange guidelines the embossing must be positioned in a particular area of the security. Since these embossings also serve as an anti-forgery feature, according to the stock exchange guidelines they must not simply take the form of a letter, but must involve a pattern as complex as possible, preferably using guilloches in order to make forgery more difficult.
The advantage of such blind embossing lies in the simplicity of checking, which can be carried out by purely tactile means without additional aids. In addition, special three-dimensional optical impressions are produced on viewing the embossing due to light/shade effects. However, the perceptibility of the embossing is greatly limited by diffuse or poor lighting.
The invention is therefore based on the problem of suggesting a data carrier with an embossing which displays an increased visual perceptibility.
According to the invention, at least part of the embossing must display the form of an inclined plane, i.e. the height or depth of the embossing decreases slowly, in relation to the rest of the surface of the data carrier, starting from a maximum value, in a predefined direction. The decrease in the height or depth of the embossing thereby preferably follows a simple mathematical function, for example a straight line, a parabola or a hyperbola, whereby the continual decrease in the form of a straight linexe2x80x94the classic decline of an inclined planexe2x80x94is preferred. For this reason, the term xe2x80x9cinclined planexe2x80x9d is used in the following for the decrease in the height or depth of the embossing in accordance with the invention, but this is not intended to be restricted simply to the classic straight-line decrease, but covers all other possible forms of the declining course. The embossing can take place in such a way that the embossed structures are raised in relation to the unembossed surface of the data carrier or can form indentations. A combination of both within an embossing is also possible. The lateral dimensions and the height or depth of the embossing are so dimensioned that no optical diffraction effect occurs.
According to a preferred embodiment, the embossing consists of several partial areas in the form of inclined planes. In this way, a piece of information which is to be embossed can be created from several inclined planes. Due to the variation in the height of the embossing within a partial area and the differences in the embossing height between different partial areas, in addition to the usual light and shade effects, contrasts easily perceptible to the human eye are created which make the embossing as a whole more distinctive and thus easier to perceive. Since any desired alphanumeric characters, patterns or other graphic representations can be created with the aid of partial areas in the form of inclined planes, it is possible to create very complex and complicated embossing patterns which additionally increase security against forgery. The dimensions of the individual inclined planes must simply be chosen in such a way that each plane is easily recognisable at a normal viewing distance without any aids. All the inclined planes used can thereby display the same type of height profile, i.e. the gradient of embossing heights/depths is the same in all partial areas, for example straight-line or parabolic in form. However, any mixtures of planes of differing inclination can also be used, whereby not only the form of the height profile can be varied, but also individual parameters within a profile. For example, inclined planes can be used whereby, though all the inclined planes display an embossing height profile in the form of a straight line, the angle of inclination of these straight lines varies. However, each embossing features at least one partial area or inclined plane the angle of inclination of which is less than 10xc2x0 in relation to the surface of the data carrier and which has a lateral dimension in the direction of the greatest inclination of more than 1.5 mm. In the case of a curved embossing height profile which does not display the form of a straight line, the angle of inclination is defined between the surface of the data carrier and the straight line produced by the connecting line between the starting point and the point with the maximum embossing height or depth.
Nor does the maximum embossing height or depth, which can be up to 250 xcexcm, necessarily need to be identical for all inclined planes. In order to increase security against forgery further, the inclined planes can be overlaid with additional embossing structures.
For reasons of clarity, only embodiments with raised embossing which features inclined planes with a straight-line height profile are chosen for the following explanations.
The invented embossing can be produced using any type of embossing tool. However, it is preferably created using the intaglio imprinting method. For this purpose, the embossing structures are engraved in a metal plate using a known method. A computer-controlled process for manufacturing such intaglio printing plates is described in WO 97/48555, for example. During the printing process, the paper is pressed into the depressions in the engraved metal plate and in this way permanently deformed. To create a blind embossing, these printing plates are not filled with ink during the printing process but are simply used to deform, i.e. emboss, the document material, for example paper.
According to a preferred embodiment, the embossing consists of several partial areas in the form of inclined planes which directly adjoin one another and the inclination of which runs contrary to one another. The planes can thereby be arranged next to one another in such a way that one inclined plane declines in one predetermined direction while the inclined plane arranged next to it rises, in a wedge form, in this direction.
According to a further embodiment, the inclined planes can also adjoin one another in such a way that they quasi overlap or would interpenetrate one another if extended. Two adjoining inclined planes thereby form a V-formed height profile, for example. Several, e.g. three or four, directly adjoining inclined planes can be arranged and aligned with one another in such a way that they form a pyramid.
Advantageously, a data carrier can also feature several embossings spaced at intervals from one another. According to a preferred embodiment, at least one inclined plane continues over several embossings, especially adjoining ones.
According to a further preferred embodiment, at least one part of the embossing displays the form of an inclined plane and, in addition, the embossed area of the data carrier features at least one coating or a sequence of coatings the optical effect of which varies depending on the viewing angle. Optically variable materials such as interference coatings, liquid crystal coatings or coatings which display diffractive structures display a change in colour when the viewing angle is altered, which cannot be reproduced with copying machines. They are therefore frequently used as anti-copying elements. If such coatings are provided in the area of the invented embossing, then a clearly perceptible alteration of the viewing angle occurs due to the height profile of the inclined planes, i.e. colour differences occur along the height profile of the embossing which make the embossing stand out against the unembossed surroundings and thus make it more easily perceptible.
A similar effect occurs if highly-reflective coatings, e.g. metallic coatings, are featured in the area of the invented embossing, because at the angle of incidence the highly-reflective coatings appear very bright and shiny, whereas at all other angles they appear darker and less brilliant. Because of the height profile of the inclined planes, certain areas of the embossing appear bright and shiny under a particular viewing angle, whereas other areas appear darker. In this way, an additional contrast is created which makes the embossing stand out better.
The aforementioned optically-variable coatings can be applied to the data carrier using any known method. For example, they can be prepared on a different substrate and then transferred to the data carrier using a transfer process. The prepared substrate material is thereby brought into contact with the data carrier via an adhesive coating and bonded with the data carrier, possibly under the application of heat and pressure. The substrate is then pulled off, whereas the transferred coating remains on the data carrier.
Depending on the material which is to be transferred, the substrate material must be treated with different sequences of coatings during preparation. For example, in the case of diffractive structures, the substrate material is usually given a plastic coating in which the diffractive structures are embossed in the form of a relief. A thin coating of aluminium is then vapour-deposited onto this relief and finally covered with a coating of adhesive. However, under certain circumstances, further coatings can be applied to the substrate material and transferred to the data carrier. A variety of methods for the manufacture of substrate materials with optically-variable coatings is known from the prior art, for example from DE 29 07 186 C2, US-A-3,858,977, EP 0 420 262 A1, EP 0 435 029 B1.
However, the coatings can also be applied in the form of coatings of coloured ink. In this case, the coatings creating the optically-variable effect contain pigments which are mixed with usual printing ink binding agents and squeegeed or printed onto the data carrier. Interference coating pigments are, for example, sold by the company Merck under the name IRIODINE(copyright) or by BASF under the name PALIOSECURE(copyright).
Further embodiments and advantages of the invention are explained with reference to the figures. It should be pointed out that the figures do not show a true-to-scale representation, but are simply intended to illustrate the invention.